Low brightness functional pigment from process by-product

Abstract

A low brightness pigment and method is provided from a heretofore rejected waste kaolin stream. Kaolin processing rejects are high in iron-stained TiO 2 . After separating the stained TiO 2 from the high brightness kaolin and concentrating the resulting fraction, the material can be processed to produce a low brightness pigment suitable of many applications where lower brightness is desirable, such as coating paper board without mottling.

We claim: 
     
       1. A paper product which includes a low brightness, high yellow index kaolin pigment from a kaolin clay containing iron-stained TiO 2 , the pigment produced by the method comprising: dispersing the kaolin clay in water to form a kaolin dispersion;   separating the kaolin dispersion into an aqueous high brightness fraction and an aqueous lower brightness fraction, the lower brightness fraction having a TiO 2  content substantially between 5-12% by weight dry clay and an Fe 2  O 3  content substantially between 0.5-2.5% by weight dry clay;   concentrating the lower brightness fraction to form a kaolin suspension containing kaolin particles and iron-stained TiO 2  particles;   dispersing the concentrated kaolin suspension with a dispersion agent;   diluting the dispersed kaolin suspension;   flocculating the diluted suspension and filtering the flocculated suspension to form a filter cake thereby removing excess salts.   
     
     
       2. An improved coated paper or paperboard comprising: a paper or paperboard base stock having a sufficiently low brightness to induce a mottled appearance if coated directly with a high brightness finish coating;   a high opacity, low brightness precoating on the base stock, the precoating containing an uncalcined low brightness kaolin pigment having a TiO 2  content of 5-12% by weight of dry clay and an Fe 2  O 3  content of 0.5-2.5% by weight of dry clay, the kaolin pigment having a TAPPI brightness substantially between 60-80; and   said high brightness finish coating thereafter placed upon the precoating to produce a finished coated paper or paperboard sheet having a reduced mottled appearance.   
     
     
       3. A coated woodfree grade paper having a reduced brightness, comprising; a woodfree grade base sheet having a base brightness; and   a paper coating placed upon the base sheet, the coating including calcium carbonate particles having a high brightness and a selected amount of an uncalcined, low brightness kaolin pigment having a TiO 2  content of 5-12% by weight of dry clay and an Fe 2  O 3  content of 0.5-2.5% by weight of dry clay, the uncalcined kaolin pigment having a TAPPI brightness substantially between 60-80, the amount of uncalcined low brightness kaolin pigment selected to variably reduce the brightness of the calcium carbonate particles resulting in a coated woodfree grade paper having a selected brightness greater than the base brightness and less than the high brightness.